To work around this, Tony incorporated a haptic feedback system into his suit which simulates how much force the suit itself is applying. That way he knows whether he's giving something a gentle nudge or is going to send it flying. So yes, he exerts himself, but its entirely for usability and not some sort of limitation of the suit itself.

you do often see stark bracing himself when firing the repulsors. And there's the part where he uses them to fly.

Tony Stark is indirectly responsible for both villains in the Spider Man MCU movies, Vulture and Mysterio's turn to villainy. In Vulture's case, he lost his job when Tony and the U.S. government shut down his business and became a black market arms dealer to feed his family.

Nope! The original Arc reactor was poisoning Tony because it was based on an imperfect design created by his Father, Howard Stark. That Arc reactor was based on the Tesseract. Tony's new Arc reactor was no longer poisoning him but it still wasn't unlimited energy.

Following his fight against Stane, Stark publicly revealed himself as Iron Man. Fresh off from defeating enemies all over the world, Stark found himself dying due to his own Arc Reactor poisoning his body, all while he was challenged by Ivan Vanko who attempted to destroy his legacy.